An A/D conversion circuit is used in digital signal processing of information which is sent from various sensors that output analog values, and is used in various devices that include detection circuits, control circuits, and the like. A conventional A/D conversion circuit incorporated in a consumer instrument such as a digital camera compares an analog signal inputted thereto from various sensors with a reference voltage, and binarizes the voltage signal for changing the voltage signal to a digital signal. Moreover, when the change in the analog signal is minor, an analog amplification circuit such as an operational amplifier is used to amplify the analog signal to get the required voltage range, and thereafter the A/D conversion circuit binarizes this signal to get a digital signal.
An A/D conversion device that combines an analog calculating circuit and an A/D conversion circuit has problems of quality and cost. As examples of quality problems, circuit characteristics such as the fluctuate of the amplification rate and the gain due to temperature characteristics which are specific to the analog amplification circuit, making it difficult to obtain a precise output digital signal value, and the power consumed by the entire A/D conversion device increases due to the steady-state current required to drive the analog amplification circuit. An example of a cost problem is that, since a transistor required for the analog amplification circuit has a larger element size than a metal oxide semiconductor (MOS) transistor generally used in digital circuits, the circuit area when integrating on one chip is larger, making it difficult to reduce the cost. Meanwhile, to accompany higher performance of systems in the practical sphere, A/D conversion devices need greater precision, and there is a demand for high bit resolution.
In response to such demands, an time A/D conversion circuit disclosed in Patent Literature 1 employs an entirely digital circuit to constitute a function of encoding a pulse phase difference that includes a ring delay line, a counter, a latch circuit, a pulse selector, and encoder, and a subtraction circuit. According to this technology, since high bit resolution can be realized by an extension of the delay line and the like, a desired bit resolution can be obtained with a digital circuit, without using an analog amplification circuit.
Moreover, since an analog amplification circuit is not used, effects are obtained of maintaining product quality by suppressing change in circuit characteristics affected by temperature characteristics which are unique to the analog circuit, and also of lowering cost as a result of reduced power consumption and higher integration.